Mineral or ceramic powder-filled, metal-sheathed cables and mechanisms for making them are well known in the art. Thompson, in PCT patent application PCT/AU90/00198, teaches the extruding of a mixture of a ceramic powder and binder onto a conductor, then enclosing the wire and ceramic powder in a metal sheath after the binder is removed by heating. In the alternative, Moore et al, in U.S. Pat. No. 5,122,209, teaches a mechanism for applying a metal sheath about a plurality of conductive wires having insulating jackets. A spring steel strip is used to displace the wires away from the region where the metal sheath is welded.
Holmgien et al, in U.S. Pat. No. 4,629,110, teaches a method for making powder-filled tubular welding electrodes. A pressurized gas is introduced into the filling conduit and is evacuated by a cylindrical duct formed between the filling tube and the welded tube.
Gill, in U.S. Pat. No. 4,512,827, teaches a fill tube for filling a seam-welded tube with a powdered insulating material. The fill tube has a pair of vertical tubular wire guides which extend the length of the fill tube. The fill tube also has a longitudinal gas delivery tube provided along one edge of the fill tube which is used to deliver argon gas to the weld area to prevent contamination of the weld.
Lewis, in U.S. Pat. No. 4,269,639, also teaches a mechanism for making mineral insulated cables. Like Gill, the fill tube taught by Lewis has a pair of tubular wire guides which extend downstream of the end of the powder fill tube and are aligned within the metal sheath by at least one spacer. One of the tubular wire guides and the powder fill tube have an elongated aperture through which an inert gas is emitted between the powder fill tube and the metal sheath in the vicinity of the weld.
What is needed is a fill tube which eliminates the tubular wire guide and eliminates the requirement of providing an inert gas between the powder fill tube and the metal sheath in the vicinity of the location where the weld is being made.